@linaria/shaker removes specific code

[layershifter]

Environment

• Linaria version: @linaria/shaker@4.0.0-beta.0
• Bundler (+ version): N/A
• Node.js version: N/A
• OS: N/A

Description

This bug is a regression (#861). The problem comes with compiled code, the minimal input is:

exports.__linariaPreval = [
  _wrap(() => ({
    root:
      ((_a = {}),
      (_a[':hover .' + switchClassName] = {
        ':before': {
          backgroundColor: 'red',
        },
      }),
      _a),
  })),
];

After the plugin 💥

exports.__linariaPreval = [_wrap(() => ({
  root: _a = {}
}))];

(while the object should remain the same 🐱 )

Reproducible Demo

https://stackblitz.com/edit/node-clu7gg?file=index.js,code.js,package.json